1. Field of the Invention
The present invention relates generally to improvements for tufting machines, and specifically relates to a yarn saving apparatus for tufting machines which inhibits the tufting of a carpet backing web along its outer longitudinal borders by selectively withholding yarn from selected outer groups of needles of a shiftable needle bar, thereby reducing the wastage of yarn which otherwise would be tufted onto the longitudinal borders and cut off when the carpet is trimmed to remove the borders.
2. Description of the Prior Art
In the tufting of pile fabrics, and particularly carpets, a series of needles are often positioned in a needle bar to carry pile yarns through a backing web or fabric which is advanced over a throat which receives the needles as the web is penetrated. Oscillating loopers positioned underneath the throat engage loops of pile yarn to hold the yarn as the needles are withdrawn, and oscillating knives may be positioned to provide cut pile, if desired.
Many conventional tufting machines often employ laterally shiftable mechanisms for repetitively changing the relative position of the needles and backing web to provide a pattern effect, to eliminate lines or streaks in the fabric which are especially noticeable with multi-colored yarns, and to break up the noticeable alignment of longitudinal rows of tufting that detract from the appearance of the carpet. Some of these mechanisms are shiftable needle bars, while others include shiftable backing web carriers. For example, U.S. Pat. Nos. 3,109,395 to Batty, 3,203,388 to Parlin, 3,964,407 to Ingram et al., 3,301,205 to Card, 3,026,830 to Bryant, and 3,964,408 and 3,972,295 to Smith disclose various mechanisms which shift the needle bar laterally as the needle bar is reciprocated toward and away from the web to cause the needles mounted on the needle bar to penetrate the web.
Generally, only a limited amount of lateral shifting is possible in shifting mechanisms due to physical limitations on the length of the needle bar or on the parameters of cam devices which are commonly employed to effectuate shifting. It is quite common to find that the relative shift between the backing web and the needles is limited to less than about six gauge spaces, that is, lateral spaces between needles. In such devices, the pattern effect produced adjacent to the outer longitudinal border of the backing web is a "wave line" of tufting, or a wave of tufted area which borders on a non-tufted portion of the backing web immediately adjacent to the longitudinal border of the backing web. For example, FIG. 28 of U.S. Pat. No. 3,249,078 to Nowicki and FIG. 6 of U.S. Pat. No. 3,203,388 to Parlin, the disclosures of which are incorporated herein by reference, show wave lines of tufting from the top surface and undersurface, respectively, of carpets which have been laterally shifted a plurality of gauge spaces. It will be understood that the lateral shifting occurs across the entire transverse width of the backing web, and that the wave line itself is most apparent only at the outer longitudinal borders of the backing web which are tufted by groupings of needles at the ends of the needle bar.
In order for the carpet to be commercially saleable, the wave line of tufting on the outer longitudinal border of the backing, together with the non-tufted portion of the backing web adjacent to the edge of the carpet (collectively, the "wastage area") must be cut off. Inevitably, there is wastage of both tufting yarn and of backing web material. It is highly desirable for the patterning effects, streak elimination, and row alignment break-up which result from lateral shifting to dominate the carpet, yet it is also desirable to eliminate the wastage of yarn which is also a result of the shifting. No prior art devices appear to provide a solution to the problem of wastage while maintaining the beneficial effects of lateral shifting.
It is known in the art that various pattern effects can also be produced by varying the height of the loop of pile yarn. Various methods have been proposed for controlling the height of the loop. For example, U.S. Pat. No. 3,249,078 to Nowicki discloses a method for tufting which combines lateral shifting of a needle bar with pile height control by a "bar type" pattern attachment yarn feed mechanism such as that shown in U.S. Pat. Nos. 2,853,033 and 2,853,034 to Crawford. Nowicki, U.S. Pat. No. 2,912,945, discloses a pattern attachment for tufting machines which controls pile height by means of a contoured feed roller. Methods for making high and low level pile heights for patterning by selective tensioning or locking of the yarn being fed to the tufting needles are taught in U.S. Pat. Nos. 2,876,183 to Parlin, 2,876,441 to Boyles, 2,842,079 to Rice, 2,782,905 to Smith, 2,940,405 to Parlin, 3,334,601 to Ellison, 3,110,276 to Penman, 2,866,424 to Masland, and 2,912,945 to Nowicki.
Control of pile height may also be achieved by a related technique in which yarn is fed to tufting needles by a speed control apparatus which selectively feeds yarn at a first rate which produces a tuft of a given height, or at a second rate, slower than the first, which produces shorter tufts than the tufts of the given height. For example, Nix, U.S. Pat. No. 2,875,714 shows that high and low loops can be formed by feeding the pile yarns over high speed and low speed rollers which alternately provide "full feed" and "starving feed" to groups of tufting needles thereby forming alternate rows of high and low pile loops. U.S. Pat. Nos. 2,862,465 to Card, 4,193,358 to Woodcock, 2,880,684 to Masland, 3,263,631 to Freeman, 2,966,866 to Card and 2,954,865 to Hackney teach that pile height may be controlled in this manner. In these patents, different heights of pile loops occur because the amount of yarn fed at the slower rate is insufficient to form a loop corresponding to the maximum depth of needle penetration, causing yarn withdrawal or "robbing" from a previously formed loop. By selectively controlling the rate of yarn feed, patterns having varying yarn height can be tufted.
No known prior art devices, however, disclose any methods or devices which allow patterning across the transverse width of the backing but which may be coordinated with the lateral shifting of the needle bar so that yarn robbing, tensioning, or withdrawal occurs only at the outer longitudinal edges of the backing web independently of any patterning control. If tufting can be inhibited or prevented at the edges when the needle bar extends over the wastage area independently of the patterning, the yarn which would otherwise be wasted as the outer groups of needles tuft the wastage area can be saved.